1. Field of the Invention
This invention relates generally to an apparatus used for digital painting and, more specifically, to an apparatus that employs a metering device for metering a quantity of paint to be deposited on a surface to be painted and that deposits the metered quantity of paint on the surface.
2. Background of the Invention
As computer technology has advanced, the ability to view high resolution graphics has improved and the resolution and speed capabilities of color printers have increased to enable reproduction of photorealistic images. One of the more significant and lucrative printer technologies to be developed in recent years is the ink jet printer that mixes several colors, typically cyan, magenta, yellow and black, on the paper to form a color image. Conventional ink jet printing heads include a plurality of nozzles and thermal elements. Ink is expelled from the nozzles in a jet by bubble pressure created by heating the ink by the thermal elements while the nozzles and thermal elements are in close proximity. One such inkjet printing head, as described in U.S. Pat. No. 5,121,143 to Hayamizu, includes a thermal head member having at least one thermal element consisting of a plurality of thermal dot elements and a plurality of electrodes of different widths connected to each thermal element whereby different widths of heated portions of the thermal element are obtainable to vary the amount of ink jetted in one dot. Another such ink jet printing head is described in U.S. Pat. No. 4,731,621 to Hayamizu et al.
Another type of print head is disclosed in U.S. Pat. No. 4,764,780 to Yamamori et al. in which an ink ejection recording apparatus includes a plurality of ink ejection heads connected to an ink tank, each of the ink ejection heads having an ink nozzle through which minute ink droplets are discharged in accordance with an electric signal and an air nozzle opposing the ink nozzle and adapted for forming an air stream which accelerates the ink droplets toward a recording medium.
Typical desk top ink jet printers for home or office use are relatively inexpensive but are usually limited to printing on standard office size sheets of paper, such as 8 xc2xdxc3x9711 or similar standard sizes. Printers that can accommodate larger formats such as poster-sized sheets, however, are currently thousands of dollars to purchase and machines that can print billboard-sized sheets are typically tens of thousands of dollars.
Some wide format printers are able to accommodate 16 feet or wider substrates such as films, paper, vinyl, and the like and can print 300 ft2 per hour, depending on the resolution of the print. Such machines sometimes employ piezo printhead technology that employs several printheads per color with numerous nozzles per printhead to deposit ink onto the print medium. Another approach is to employ air brush technology in which inks are metered by valves and/or pumps and deposited onto the substrate. The quantity of ink pumped for each color and the position at which it is deposited on the print medium is typically computer controlled. The print medium is typically provided on a roll in which unmarked medium is fed under the print head and printed medium is re-rolled once the ink has had sufficient time to dry. Large format printers using air brush technology typically have a resolution of up to approximately 70 dpi.
In addition to the cost of the machine itself, which employs relatively small orifices, valves and nozzles for depositing the desired quantity and color of ink on the print medium (e.g., paper), very fine grade inks are used in which particle sizes within the inks are kept to a minimum to help keep the orifices, valves, and nozzles of the ink system from becoming clogged. Such inks are expensive and are not very cost effective for painting billboard sized prints. Despite the high quality and expense of ink products, clogging of the printhead is still a problem in current printer technologies.
Many large format printers also use water-based inks that may not be suitable for outdoor use. Accordingly, special waterproofing systems and techniques must be employed such as treating the printing medium with a substance that binds with the ink once deposited to form a waterproof mark or laminating the print with a weatherproof film. These weatherproofing techniques and processes add expense to the cost of each print.
Thus, it would be advantageous to provide a paint injector or print head that does not include orifices and/or nozzles through which the ink or paint must flow and, thus, is not limited by paint particle size or large particle contamination and is relatively insensitive to the physical properties of the paint. It would also be advantageous to provide a device that can use paints and inks already designed for the sign and art industries and that can be employed to digitally print on large format media.
It is an object of the present invention to provide a paint injector that can print with many forms of liquid printing materials such as paints and inks.
It is another object of the present invention to provide a paint injector that is relatively simple in construction and relatively inexpensive to manufacture.
It is yet another object of the present invention to provide a paint injector in which the liquid printing material is metered through computer control.
It is still another object of the present invention to provide a plurality of paint injectors in a print head, each paint injector containing a different color, and employing the print head to create a digital image on a print medium.
Accordingly, a paint injector is provided comprising an air nozzle that directs a jet of air across a moving member, the member having ink, paint, or other similarly pigmented liquid material disposed thereon. The air jet pulls the paint off of the member and onto a print medium, such as paper, vinyl, film, or other print media known in the art. Preferably, the segment is a continuous loop of material that is sequentially moved in front of the air jet by at least one wheel around which the loop is disposed. Thus, as the loop is advanced in front of the air jet, paint thereon is blown off of the loop and onto the print medium.
In a preferred embodiment, a miniature wire cable is employed to bring ink or paint contained within a reservoir in proximity with an air stream where it is carried to a print medium. A microprocessor or other controlling device controls the cable so that the speed of the cable""s advance through the air stream meters the quantity of paint injected into the air stream. As the cable is advanced through the reservoir, a coating of paint clings to the cable, the thickness of the coating being controlled to a degree by the viscosity of the paint. In addition, a mechanical metering device, such as a scraper riding proximate to or in contact with the cable as it is advanced, may be employed to control the thickness of paint on the cable before it enters the air stream. The cable, having a coating of paint thereon, is then drawn into close proximity to one or more jets of air. As the paint on the cable reaches the jet of air it is pulled or blown off the cable into the air stream until it impacts the print medium. In order to keep the cable positioned in front of the air stream, a cable guide may be employed proximate to the air nozzle to prevent the cable from being forced away from the air stream and to reduce vibration of the cable in the air stream.
The cable is preferably drawn through the paint reservoir and thus coated with paint by being disposed around a pulley or wheel driven by a motor and around an idler or guide that is at least partially immersed in paint. A controller, such as microprocessor or other computing device, controls the advance of the motor and thus movement of the cable. In addition, the controller can control movement of the paint injector as it is swept across a print medium. By utilizing a plurality of paint injectors in a print head, each containing a different color of paint, and by controlling and coordinating the metering of the paint and the position of the print head, a digital image can be created on the print medium.